The present invention relates to apparatus for quickly and precisely holding a workpiece for machining operations and, more particularly, to a power driven clamping device for securing the workpiece to a support and a mechanism for sensing the proper positioning of the workpiece and consequently actuating the clamping device.
Many precision machining operations can be performed by machines for which the workpieces are placed by hand onto a support and then fixed to the support. Although there is seldom a problem with securely fastening the workpieces to the support, some clamping devices have tended to slightly twist, deflect or otherwise distort the workpiece as they secure it for machining, which causes inaccuracy in the finished pieces. Furthermore, the hand placement of the workpieces is sometimes done carelessly, resulting in incorrectly positioned and, therefore, improperly machined workpieces. Even when done with care, a workpiece can be slightly out of position by an amount not apparent to the eye but sufficient to cause improper machining. In addition, many known workpiece holders have pivoting arms employing pivot pins which tend to rust in place over time, making removal of the pivoting arms and repair or rearrangement of the workpiece holder difficult.